The use of reinforced composite materials to produce structural components is now widespread, particularly in applications where their desirable properties are sought. Depending on the material, those properties include light weight, strength, toughness, thermal resistance, self-support and adaptability in terms of being formed and shaped. Such components are used, for example, in aeronautical, aerospace, satellite, battery, recreational vehicles (as in racing boats and automobiles), and other applications.
Often, the desired property in a material used to make reinforcement preforms is high strength. However, a typical characteristic of materials which exhibit that property is that their highest strength is in the direction of the long axes of the constituent fibers or filaments. For this reason, it is desirable to fabricate such reinforcement preforms to so orient the reinforcement preform constituent materials so that their long axes are substantially in the same direction as will be the forces to which the finished components will be subjected. Since those forces may be multi-directional, in some applications the reinforcement material may be oriented multi-directionally, typically in a lamination of two or more plies, to render the strength properties of the finished component operable in more than one direction, even to the point of being quasi-isotropic. By this means, such forces may be caused to be borne primarily by fibers whose long axes are oriented in the direction those forces, thus enabling the strengthening constituents of the composite structures to present their highest load-bearing capabilities to them.
Frequently, it is desired to produce components in configurations that are other than such simple geometric shapes as (per se) plates, sheets, rectangular or square solids, etc. A way to do this is to combine such basic geometric shapes into the desired more complex forms. One such typical combination is made by joining reinforcement preforms made as described above at an angle (typically a right-angle) with respect to each other. Such angular arrangements of joined reinforcement preforms create a desired shape which include one or more end walls or "T" intersections between the preforms. This arrangement may strengthen the resulting combination of reinforcement preforms and the composite structure that is produced against deflection or failure upon being exposed to exterior forces, such as pressure or tension. In any case, a related consideration is to make each juncture between the constituent components as strong as possible so forces cannot pull the composite article apart. Otherwise, given the desired very high strength of the reinforcement preform constituents per se, weakness of the juncture compared to that of each of the combined elements per se becomes the weak link in the structure.
An example of this type of intersecting configuration is where one of two constituents is an elongated, flat, planar rib that is oriented substantially at a right angle to and across a mid-span location of the other constituents, which is a planar sheet. In this structural arrangement, it is desirable to inhibit or prevent the planar sheet from deflecting objectionably or failing as pressure is applied in the direction of the width dimension of the reinforcing rib. Also, it is desirable to provide a juncture between intersecting elements (such as planar sheets per se, sheets and strips or other shapes, etc.) which will not fail when forces are applied to one of the intersecting elements in directions away from the other element which it intersects.
Various proposals have been made in the past for making such junctures. The forming and curing of a first panel element and a second angled stiffening element has been proposed, with the latter having a single panel contact surface, or otherwise bifurcated at one end to form two divergent, co-planar panel contact surfaces. The two components are then joined by adhesively bonding the panel contact surface(s) of the stiffening element to a contact surface of the other component using thermosetting adhesive or other adhesive material. However, when tension is applied to the cured panel or the skin of the composite structure, loads at unacceptably low values result in peel forces which separate the stiffening element from the panel at their interface since the effective strength of the join is that of the reinforcement material and not of the adhesive.
To use metal bolts or rivets at the interface of such components is also unacceptable because such additions at least partially destroy and weaken the composite structures themselves, add weight, and introduce differences in the coefficient of thermal expansion as between such elements and the surrounding material.
Other approaches to solving this problem have been based on the concept of introducing high strength fibers across the join area through the use of such methods as stitching one of the components to the other and relying upon the stitching thread to introduce such strengthening fibers into and across the juncture site. One such approach is shown in U.S. Pat. No. 4,331,495 and its divisional counterpart, U.S. Pat. No. 4,256,790. These patents disclose junctures between a first and second composite panels made from adhesively bonded fiber plies. The first panel is bifurcated at one end to form two divergent, co-planar panel contact surfaces, each joined to the second panel by stitches of uncured flexible composite thread through both panels. The panels and thread have then been "co-cured", i.e., cured simultaneously. This proposal is inadequate as evidenced by subsequent efforts to cope effectively with the problem of join strength.
U.S. Pat. No. 5,429,853 proposes ajoin between reinforced composite components that are in the form of a panel and of strengthening rib. One of the components is in the form of an elongated strip which is angled linearly to form a panel contacting bearing flange that is continuous with the rest of the rib which forms a stiffening flange. As disclosed, two such ribs may be joined to each other with their stiffening flanges back to back. The effect of this is effectively to create a bifurcated element having the panel contacting surfaces across the top of the "T" so formed. The bearing flange(s) of the stiffening rib are placed in contacting juxtaposition with a the surface of the panel, and the two elements (i.e., the rib and the panel) are then joined by a fibrous "filament" or thread which is inserted vertically through the panel and into the reinforcing member, with some of the filament extending into and in line with the main body of the "stiffening flange" i.e., the portion of the stiffening rib which is vertical to the plane of the panel element. The asserted effect of this is to have some of the fibers that have been introduced by the filament extend from the panel element into the stiffening flange portion of the stiffening rib. While perhaps efficacious for certain purposes, such prior art constructions still do not exhibit the desired amount of strength against failure of such joins with consequent separation of the constituent reinforced elements from each other.